Electrical resistance device



Aug. 5, 1930. F. R. FRIEDRlCH ET AL 1,772,231

ELECTRICAL RESISTANCE DEVICE Filed Aug. 12, 1926 A ///////l VII/I/l/I/I/I/l/Il/I/II////// VI/IA BY 8. v ATTORNEY Patented Aug. 5, 1930 UNITED STATES PATENT OFFICE FRITZ R. FRIEDRICH AND FRANCIS FRIEDRICH, OF NEW YORK, N. Y.

ELECTRICAL RESISTANCE DEVICE Application filed August 12, 1926. Serial No. 128,754.

This invention relates to electrical resistance devices and more particularly to variable resistances adapted for use, for example, in the gridleak circuit of wireless receiving apparatus.

One of the objects of the inventlon is to provide a device of the above nature which is practical and highly efiicient. Another object is to provide a device of the above nature wherein the effective resistance is capable of very accurate adjustment. Another ob ect is to provide a device of the above nature the accuracy andefiiciency of WlllCh are notaffected by conditions of use. Another ob ect is to provide a device of the above nature which is simple and inexpensive and wlnch is long-lived. Other objects will be n part obvious or in part pointed out hereinafter. The invention accordingly consists in the 20 features of construction, combinations of elements and arrangements of parts as W1ll be exemplified in the structure to be hereinafter described and the scope of the apphcation of which will be indicated in the followlng claims.

In the accompanying drawing in which are shown one or more of the various posslble embodiments of the several features of th1s invention,

Figure 1 is a longitudinal section showing one form;

Figure 2 is a transverse section taken substantially along the line 2-2 of Flg. 1;

Figure 3 is a longitudinal section showing a modified construction, and

Figure 4 is a section taken substantially along the line 4-4 of Fig. 3. Similar reference characters refer to similar parts throughout the several views of the drawing.

Referring now to the drawing in detail and first to Figure 1, there is shown a container or casing which is made of a suitable insulating material such as rubber or the like and which preferably takes the form of an elongated cylinder or tube. At one end of the tube is a metal member 11 which projects into the interior of the tube and preferably takes the form of a plug threaded thereinto and closing the end of the tube. This metal member or plug 11 is provided with a suitable connector for connecting an electrical conductor thereto. This connector conveniently takes the form of a metal plate 12 which may be clamped between the plug and the end of the tube and to which the electrical conductor may be secured by soldering or other suitable means.

In the opposite end of the tube 10 is a metal member 13 which preferably takes the form of a bushing threaded into the end of the tube. This bushing 13 is provided with a connector similar to that of the metal member 11 attaching thereto an electrical conductor. This connector conveniently takes the form of a plate 14 similar to the plate 12 and clamped between the bushing 13 and the end of the tube 10.

The resistance device when in use may be mounted upon a panel 15. For this purpose the bushing 13 is provided with an outer threaded projection 16 of reduced diameter. A nut 17 threaded upon the part 16 clamps the panel 15 and supports the device in position for convenient operation.

- Passing through the bushing 13 and rotatably supported therein is a shaft or spindle 18. The outer end of the spindle carries a suitable handle 19 by means of which it may be rotated conveniently, and the portion of the spindle within the tube 10 is threaded. The spindle 18 is held against axial movement by a bushing 20 which is threaded into the inner end of the bushing 13 and coacts with a collar 21 on the spindle. Between the bushing 20 and the collar 21, and about the spindle 18, may be inserted a suitable packing 22 for the purpose of preventing possibility of leakage outwardly along the spindle of the material contained in the tube 10. This material will be described presently.

Within the tube 10 and in threaded engagement with the spindle 18 therein, is a metal member 23 which has an arm 24 projecting longitudinally of the tube toward the end thereof and the metal member 11. Against the inner surface of the tube are a pair of spaced parallel guides 25 and 26 which are preferably integral with the part 20 and between which a part of the member 23 is positioned and which thus hold the member 23 against rotation. By turning the spindle 18 by means of the knob or handle 19, the member 23 is thus advanced along the spindle 18 and the part 24 thereof moves lengthwise of the tube and toward and away from the metal plug 11.

The remaining space within the tube 10 between the plug 11 and the bushing 20 is filled with a mass of conducting material 27 of high electrical resistance. Preferably this conducting material is in the form of a paste. It may be of a thick and plastic consistency or it may be thinner and in an almost i'luid state. The material comprises preferably amixture of a plastic and practically non-conductive material with a finely divided conductive material, the two being thoroughly and uniformly intermingled. A mixture of petroleum jelly with finely divided carbonv in proportions on the order of one part of petroleum jelly to three parts of carbon is found to be highly satisfactory. The carbon is preterably of the kind used for electrodes in the electrical arts, such as the carbon electrode of a dry cell, or the carbon used in compressible carbon pile resistance, but appropriately pulverized. A resistance material of this nature is substantially permanent and unvarying in its resistance properties and is unailected by aging or by temperature or other conditions which are met with in use.

The end of the arm H is preferably pointed,

indicated in Figure 2, so that it readily pierces the conductin material in its movement toward the plug 11. The curren is conducted from the plug 11 through the material 27 positioned therebetween and the end of the part 2%, through the spindle 1S and thence to the terminal bushing 13. By advancing the part 24 toward the plug 11 the amount of the resistance material. through which the current is required to pass is reduced and, conversely, by moving; the part- 2-lin the opposite direction, the resistance is increased. A very line and accurate adjustment of the resistance is thus obtainable. t is to be noted that the spindle 18 does not move into and out of the tube so that the 'olume of the metal parts within the tube remains continually the same. Thus there is no compression of the plastic re .stance material which would tend to force it out of the tube and result in leakage. It is of advantage also to have the knob 19 remain continually at a fixer. distance from the panel 15 instead of moving in and out as the spindle is turned.

In Figure 3 there is shown a slightly different term of construction. The insulating tube 28 is closed at one end by a metal plug 29 and has threaded thereinto at the othtl S er end bushing 30 in which is rotatably supported spindle 31. This spindle 31 has .ae inner end thereof a hollow part 32 of enlarged diameter and interiorly threaded.

In threaded engagement with the part 32 is a member 33 which has a projecting arm 3 lprojecting toward the plug 29 and taking the form of a thin blade. A metal plate 35 is forced into the tube from the end closed by the plug 29 and comes against a shoulder 28. This plate is provided with a slot through which the blade projects. and it thus holds the member 33 against rotating while permittin it to move toward and away from the plug 29. A collar 36 "formed on the spindle and engaging the inner side oi the bushing 30. holds the spindle against axial movement.

The space within the hollow part 32 and between the plate 35 and the bushing 30 is filled with a mass of the plastic resistance material. The part 33 and the plate 35 are perforated as indicated in order to permit the resistance material to flow therethrough as the device is operated and to avoid compressing the material.

By turning the spindle the part 33 is advanced along the hollow part 32 and the blade 3% is moved through the resistance material and toward or away from the plug 29 to adjust the value of the resistance. The current is conducted from the plug 29 through the resistance material to the blade 3e, thence through the spindle part 32 to the bushing 30, the plug 29 and the bushing 30 being provided with suitable connectors 36 and 37 respectively.

From the foregoing, it will be seen that there is herein provided a device which achieves the objects of this invention and occomplishes many practical advantages. The resistance device provided is capable of extremely accurate adjustment and is of such nature that it will give uniform and dependable service indefinitely.

It is to be understood that, although the particular embodiments of the invention shown herein are suitable for use in the grid leal: circuits of wireless receiving apparatus and achieve particular advantages in such a acity, the broader features ot' the inven- 4.1011 a re applicable to a variety of uses where electrical resistance devices are employed.

As many possible embodiments may be made 01: the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbeitore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

o claim as our invention:

1. In an electrical resistance device, in combination, a container of insulating material, a mass of conducting material within said container, :1 metal plug threaded into said container and contacting said conductmaterial therein, a second metal plug threaded into said container at a point spaced from said first plug, a metal member within said container and movable through said conducting material therein toward and away from one of said metal plugs, and means projecting through the other of said plugs for moving said metal member Without causing displacement of said means relative to said plug.

2. In an electrical resistance device, in combination, a tube of insulating material, a mass of conducting material substantially filling said tube, a metal member adjacent one end of said tube contacting said conducting material therein, a metal bushing adjacent the other end of said tube, a spindle projecting through said bushing and rotatable therein but held against axial movement relative thereto, and a metal member threaded upon the inner end of said spindle and capable of being advanced along said spindle and through said conducting material toward and away from said metal member, the projecting portion of said spindle and said member threaded thereon being wholly immersed in said conducting material.

3. In an electric resistance device, in combination, a tube of insulating material, a mass of conducting material substantially filling said tube, a metal member adj acent one end of said tube contacting said conducting material therein, a metal bushing adjacent the other end of said tube, a spindle projecting through said. bushing and rotatable therein but held against axial movement relative thereto, a metal member within said tube surrounded by said conducting material and threaded upon said spindle, means adapted to hold said last metal member against rotation, said last metal member being adapted to be advanced along said spindle and through said conducting material toward and away from said first metal member, and means upon the outer end of said spindle for a turning the same.

In testimony whereof, we have signed our names to this specification this 10th day of August, 1926.

FRITZ R. FRIEDRICH. FRANCIS FRIEDRICH. 

